This invention relates to a safety device for use in a device in which the condition of a coincident focusing point of a camera is electrically detected and a photographing lens is automatically set to a desired coincident focusing point position in reference to the output of the detection.
In a conventional prior art auto-focusing device of a camera, there has already been proposed a system in which the principle of a dual image coincident type distance meter is utilized for producing the coincident focusing point signal when an image is formed by a fixed mirror of on a pair of light receiving elements and an image is formed by a movable mirror which is cooperative with the photographic lens, and thereafter the photographic lens is fixed at a position of the coincident focusing point. In this conventional system, since the image forming signal made by the movable mirror is provided after the photographic lens is started to displace its position by some driving force, such disadvantage has been found as the coincident focusing point signal is not generated either when the contrast in the object to be photographed is extremely low or when a brightness is low and a detection for the focusing point is not possible, resulting is no fixing of the photographing lens and thus said photographic lens is applied to the photographing operation under such condition as the lens is displaced to .infin. or a short distance scale.